1. Field of the Invention
This invention relates to a liquid crystal composition. Particularly this invention relates to a liquid crystal composition having an ability to indicate an antiferroelectric phase (chiral smectic C.sub.A phase, hereinafter abbreviated to "SmC.sub.A * phase"). More particularly, this invention relates to an antiferroelectric liquid crystal composition suitable for use in a liquid crystal indication element.
2. Description of the Related Art
Recently, liquid crystal displays have become widely used as indication elements, due to their thin thickness, light weight, low electricity consumption etc. However, most of these displays use TN (Twisted Nematic) type displays comprising a nematic liquid crystal. Since the driving of the indication method of the TN type is based on the anisotropy of the dielectric constant of the liquid crystal, the speed of response is slow, and an improvement is required.
In contrast, liquid crystal devices comprising the chiral smectic C phase (hereinafter abbreviated as "SmC* phase") liquid crystal, which is ferroelectric and was discovered by Meyer et. al., has a high speed response and memory characteristics which are not attained by nematic liquid crystals. Thus, the application of ferroelectric liquid crystals to a ferroelectric liquid crystal display is being vigorously researched. However, the good orientation and memory characteristics required for this indication method are difficult to realize in a real cell. For example, the cell has the problems that it is not resistant to external shocks etc., and many problems must be solved.
On the other hand, recently, an antiferroelectric phase (hereinafter abbreviated as "SmC.sub.A * phase") has been discovered which shows three stable states on the lower temperature side of said SmC* phase, by Chandani et. al. This antiferroelectric liquid crystal shows a thermodynamically stable phase wherein dipoles are arranged in antiparallel in every adjacent layer, and exhibits an electric field-induced phase transition between the antiferroelectric phase and the ferroelectric phase which is characterized by a clear threshold value and double hysteresis characteristics in response to an applied voltage. Research on a new indication method utilizing this switching behavior has already begun.